This invention relates to a system and method for controlling a clutch assembly and more particularly, to a system and method for controlling a transfer case clutch assembly which provides for a relatively smooth release of torque from the front and/or rear driveshafts of the vehicle.
Four-wheel drive vehicles typically include a transfer case which selectively transfers torque and power from the vehicle""s input shaft to a front and a rear driveshaft, thereby selectively rotating the front and rear driveshafts. The transfer case includes a conventional electromagnetic clutch assembly which typically and selectively transfers torque from a primary driveshaft (e.g., the rear driveshaft) to a secondary driveshaft (e.g., the front driveshaft), thereby reducing the torque provided to the primary driveshaft and increasing the torque provided to the secondary driveshaft. The clutch assembly is typically and communicatively coupled to a controller which determines the amount of torque that is to be provided to the front and rear driveshafts based upon vehicle sensory data, and which generates a command signal to the clutch assembly, thereby controlling the amount of torque which is provided to front and rear driveshafts.
Under certain circumstances and/or vehicle operating conditions, it is desirable to xe2x80x9creleasexe2x80x9d or disengage the clutch assembly to reduce the amount of torque which is being provided to the front and/or rear driveshaft, in order to avoid relative slip between the front and rear wheels of the vehicle. During these xe2x80x9creleasesxe2x80x9d, the clutch assembly often enters into an undesirable cycling or xe2x80x9cslippingxe2x80x9d condition that results in noise and vibration harshness (xe2x80x9cNVHxe2x80x9d) problems, which are perceived by the operator and/or passengers of the vehicle. Additionally, these undesirable cycling or xe2x80x9cslippingxe2x80x9d conditions cause premature wear to the clutch assembly, thereby reducing the operating life of the clutch assembly.
There is therefore a need for a system and method for controlling a clutch assembly within the transfer case of a four-wheel drive vehicle which allows the clutch assembly to release torque from the front and/or rear driveshafts of the vehicle in a relatively smooth manner, and which does not result in NVH problems or in premature wear to the clutch assembly.
It is a first object of the invention to provide a system and a method for controlling a clutch assembly which overcomes at least some of the previously delineated drawbacks of the prior systems, devices, and/or methods.
It is a second object of the invention to provide a method and a system for controlling a clutch assembly located within the transfer case of a four-wheel drive vehicle which allows torque to be released from the front and/or rear driveshafts of the vehicle in a relatively smooth manner and which substantially prevents undesirable and unnecessary cycling of the clutch assembly.
It is a third object of the invention to provide a system and a method for controlling a clutch assembly located within the transfer case of a four-wheel drive vehicle which allows the clutch assembly to be relatively rapidly xe2x80x9creleasedxe2x80x9d or disengaged in a manner which does not result in undesirable NVH problems or in unnecessary wear of the clutch assembly.
According to one aspect of the present invention a system for controlling a clutch assembly is provided. The clutch assembly is operatively disposed within a four-wheel drive vehicle and is effective to transfer torque between a front driveshaft and a rear driveshaft. The system includes a first sensor which measures a first speed of the front driveshaft and which generates a first signal based upon the first speed; a second sensor which measures a second speed of the second driveshaft and which generates a second signal based upon the second speed; and a controller which is communicatively coupled to the clutch assembly and which receives the first and second signals. The controller generates a first output signal based upon the first and second signals, and is further effective to determine whether a slip condition is likely to occur within the clutch assembly based upon the value of the first output signal, to selectively transmit the first output signal to the clutch assembly only if a slip condition is not likely to occur within the clutch assembly, and to generate and selectively transmit a second output signal to the clutch assembly effective to smoothly release the clutch assembly if a slip condition is likely to occur within the clutch assembly.
According to a second aspect of the present invention, a method for controlling a transfer case clutch assembly is provided. The method includes the steps of: providing a controller which generates a first clutch output signal; determining whether the first clutch output signal has exceeded an initial threshold value for a predetermined period of time; selectively transmitting the first clutch output signal to the transfer case clutch assembly if the first clutch output signal has not exceeded the initial threshold value for the predetermined period of time; determining whether the first clutch output signal has fallen below a second threshold value; selectively transmitting the first clutch output signal to the transfer case clutch assembly if the first clutch output signal has not fallen below the second threshold value; and selectively transmitting a second clutch output signal to the transfer case clutch assembly if the first clutch output signal has exceeded the first threshold value for the predetermined period of time and has subsequently fallen below the second threshold value, the second signal being effective to selectively and relatively smoothly disengage the clutch assembly.
Further objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred embodiment of the invention and by reference to the following drawings.